In recent years, the downsizing of electronic components has been increasingly demanded. As a result, the mainstream of coil components is shifting to a multilayer type.
Multilayer coil components obtained by co-firing ferrite and internal conductors have a problem that internal stress arising from the difference in thermal expansion coefficient between ferrite layers and internal conductor layers deteriorates magnetic properties of the ferrite layers to cause the reduction or variation in impedance of the multilayer coil components.
To solve such a problem arising from differences in thermal expansion coefficient causing variation in impedance of multilayer coil components, an element has been proposed in which a multilayer impedance element includes voids between ferrite layers and internal conductor layers. The voids are formed by immersing a calcined ferrite element in an acidic plating solution. With the voids present, the influence of stress due to the internal conductor layers on the ferrite layers is thereby avoided. See, Japanese Unexamined Patent Application Publication No. 2004-22798 (Patent Literature 1).
To prevent the inductance from varying due to the influence of a magnetic field, a method has been proposed in which the inductance is stabilized in such a manner that surfaces of internal conductors are corroded by impregnating a multilayer coil component (multilayer chip inductor) with a corrosive solution and voids are formed between a ceramic base and the internal conductors. See, Japanese Unexamined Patent Application Publication No. 4-192403 (Patent Literature 2).